ManyToManyField 值为 None

如何解决ManyToManyField 值为 None

我正在尝试将 ManytoManyField 用于我的 Book ，但它在网页和管理中显示 None。这是我的代码

class Category (models.Model):
    name = models.CharField(max_length=40)
    def __str__(self):
        return self.name


class Book(models.Model):

    title = models.CharField(max_length=40)
    author = models.CharField(max_length=30)
    description = models.TextField()
    category = models.ManyToManyField(Category)
    publish_year = models.CharField(max_length=5)
    language = LanguageField(max_length=40,default=False)
    age_group = models.CharField(max_length=5,choices=GROUP_CHOICES)
    downloaded_times = models.IntegerField()
    rate = models.FloatField()
    rate_times = models.IntegerField()
    rate_total = models.FloatField()
    book_image = models.ImageField(upload_to='book_cover_image',default="image.png")
    pdf_file = models.FileField(default=True,upload_to='media')


    def __str__(self):
        return f"{self.title}|-|{self.category}|-|{self.author}"

在views.py中我有

def get_queryset(self):
    query = self.request.GET.get('q')
    object_list = Book.objects.filter(
        Q(title__icontains=query) 
    )
    print(Book.category)
    return object_list

类别如下所示：

解决方法

book.category 是 manager，而不是 QuerySet，您可以使用 .all() [Django-doc] 将其转换为 QuerySet，因此：

def get_queryset(self):
    query = self.request.GET.get('q')
    object_list = Book.objects.filter(
        Q(title__icontains=query) 
    )
    for obj in object_list:
        print(obj.category.all())
    return object_list

在您使用的 __str__ 中：

def __str__(self):
    return f'{self.title}|-|{self.category.all()}|-|{self.author}'